The powered saw is an important powered tool that a surgeon employs to perform certain surgical procedures. A typical powered saw has a handpiece in which is housed either an electrically or pneumatically driven motor. The motor is attached, through a drive shaft, to a head. The head is designed to removably receive a saw blade. Actuation of the motor causes movement of the saw blade. This movement of the saw blade gives the blade the power to cut through the tissue it is employed to separate. Powered surgical saws are able to cut through both hard and soft tissue much faster, and with greater accuracy, than the manually operated saws that they have replaced. Also, it should be clear that the physical effort a surgeon has to employ to operate a powered surgical saw is much less than that used when cutting tissue with manual saws.
Some surgical saws are designed for use with flat saw blades. Typically, this type of saw blade has a base that seats in a complementary slot or opening formed in the head. The base of the blade has one or more openings or slots in which coupling members integral with the saw head seat in order to lock the blade to the head. Extending from the base, the saw blade has a main body. The leading edge of the main body is formed with teeth that perform the cutting action.
Many surgical saws are designed so that their heads and complementary blades engage in a repetitive right-left-right-left oscillating motion. More specifically, the head of an oscillating motion saw moves in either sagittally or reciprocates. When a blade is moved sagittally, it pivots in a plane parallel to the longitudinal axis of the saw head. When a blade reciprocates it moves back and forth along the longitudinal axis of the blade.
Over the past few years, it has become popular to provide powered surgical sagittal saws with heads that have tooless mechanisms for coupling the saw blades to the saws. These mechanisms often have a spring loaded device for holding the head coupling members in position that lock the saw blades in place. The coupling member is displaced from the locked state to the load state by the depression of a button also built into the saw head. One advantage of these assemblies is that they make replacing saw blades, which can occur during surgery, a relatively simple task. All one has to do is depress the button in order to move the coupling member to the unlocked state; the surgical personnel then remove one blade and insert a new blade. Still another advantage of these assemblies is that they eliminate the need to bring another tool, either a small wrench or a key, into the surgical suite. The elimination of this tool eliminates the need to have to sterilize it before an operation and the need to have to account for its presence.
While current surgical saws, with tooless heads, have proven to be useful surgical tools, there is a disadvantage associated with their use. When an oscillating motion saw with this type of head is actuated, it generates a significant amount of noise. This is because current saw blades do not tightly fit into the saw head slots in which they seat. There are two reasons for this. First, these saw heads and their complementary blades are inherently dimensioned so that there is a small interstitial gap between the blade and the adjacent walls of the saw head that define the complementary slot. This gap ensures the base of the blade can be quickly slide into and removed from the slot. Secondly, there is a slight gap due to the inherent manufacturing tolerances that arise during fabrication of these components. Consequently, each time a saw head changes its direction of motion, the inertial movement of the saw blade, which is still traveling in the first direction, causes the side of the blade to abut, slap, against the adjacent surface of the saw head. Each time this motion occurs, noise is produced. These saw blades typically oscillate back-and-forth at a rate of 10,000 to 20,000 cycles/min. The cumulative noise produced by the saw blade repetitively striking the interior walls of the saw head in which it is seated is quite noticeable.
There have been attempts to provide saw head-and-blade assemblies designed to minimize the noise produced when these components are actuated. In one such assembly, the saw head is provided with tapered pins and the base of the saw blade is provided with holes in which the pins seat. This arrangement is intended to provide a tight fit between the pins and the adjacent section of the saw blade through which the pins seat. By providing this tight fit, the post-insertion play of the saw blade is reduced. The reduction in this play reduces the incidence of the blade striking the interior walls of the saw head and the noise generated by such action. This assembly has minimized the noise associated with the actuation of a surgical saw. However, it is costly to precision machine the tapered pins used to hold the saw blade in the head.
Moreover, often a sagittal saw will include an indexing mechanism. The indexing mechanism rotates the saw head so the saw blade is in a specific angular orientation relative to a center axis that extends through the saw. The indexing mechanism makes it possible for the surgeon to best position the saw blade to accomplish the desired surgical task.
A number of known indexing mechanisms include a neck-in-collar arrangement. Thus, a neck integral with the saw head is rotatably fitted in a collar integral with the static housing of the saw. One disadvantage of known indexing mechanisms is that, for the saw head and neck to be rotated, the surgical personnel must employ a significant amount of manual force to overcome the retention mechanism used to hold the head and neck to the rest of the handpiece. Still another disadvantage of known indexing assemblies is that, over time, a corrosive bond may form between the fixed collar and the rotating neck. The formation of this bond can be accelerated by the moisture to which the saw is exposed when sterilized. When such bonding occurs, it becomes increasingly difficult to use manual force to index the saw head and neck relative to the static collar.
Also, a locking tab is normally employed in an indexing mechanism to prevent the axial rotation of the sagittal head. Known tabs loosely fit in the slots in which they are seated. This loose fit causes the tab to vibrate against the surface of the adjacent slot-defining surfaces. This contact adds to the noise produced when the saw is actuated.